1. Field of The Invention
The present invention relates to a directional control valve, so called end clutch of a hydraulic control system, for an automatic transmission vehicle and more particularly to a control means for a directional control valve with a simple construction, which can improve the performance of an automatic shift control.
2. Description of the Related Art
A conventional automatic transmission for a vehicle has a torque converter and a multiple stage transmission gear mechanism connected with the torque converter, which hydraulically actuates friction members for selecting one of the gear stages of the transmission gear mechanism in accordance with vehicle operating conditions.
A hydraulic control system pressurized by an oil pump provides working pressure required to operate the friction members and control valves.
The commonly used automatic transmission for a vehicle has a fluid torque converter which generally includes a pump impeller connected with an engine output shaft to be driven thereby, a turbine runner with an output shaft member, and a stator disposed between the pump impeller and the turbine runner, so that hydraulic fluid is circulated by the engine-driven pump impeller through the turbine runner with the aid of the stator which functions to deflect the hydraulic fluid from the turbine runner to a direction where fluid flow does not disturb a rotation of the pump impeller when fluid flows into the pump impeller.
The automatic shift is made by the operation of friction members such as clutches or a kick-down brake at each shift change. Also, a manual valve whose port is converted by selecting a position of a selector lever, is designed to be supplied with oil from and to supply the oil to a shift control valve. In a 4-speed automatic transmission, the shift control valve has an opening port made by an electronic control system.
One example of a hydraulic pressure control system of an automatic transmission for vehicles will be described in FIG. 3 which shown a circuit diagram of a conventional hydraulic control system comprising a torque converter 1 attached to an engine through the engine flexplate, and rotating at the engine speed for transmitting power of the engine to the input shaft of the transmission gear mechanism, a damper clutch control valve 2 for controlling the application and release of a damper clutch to increase the power train efficiency inside the torque converter 1, a regulator valve 5 for regulating an output oil pressure of the oil pump 4 according to the automatic transmission requirements, and a reducing valve 6 for stably regulating the oil pressure supply to a solenoid valve and the damper clutch control valve 2.
A manual valve 7, which is connected with an outlet of the oil pump 4 and is provided with the hydraulic pressure, is designed to deliver line pressure to the regulator valve 5 and a shift control valve 8. In the manual valve 7, lands are changed according to the position of a shift selector lever.
The shift control valve 8, which is operated in response to two shift control solenoid valves P and Q controlled by TCU, is designed to transmit the oil pressure selectively through a first-second speed shift valve 9, an end clutch valve 10, a second-third and a third-fourth speed shift valve 11, and a rear clutch exhaust valve 12 to a front clutch 13, a rear clutch 14, a low and reverse brake 15, a kick down servo brake 16, the end clutch 17, and the like.
An N-D control valve 18 is connected to the rear clutch 14. An N-R control valve 19 is connected to the first-second speed shift valve so as to reduce an impact caused by the shift.
Also, a pressure control solenoid valve 20 is connected to a pressure control valve 21 to reduce a shock produced by the control at the time of shifting.
The 4-speed automatic transmission described above uses the end clutch valve 10 to deliver the power of the input shaft to a carrier of a planetary gear unit in the fourth speed.
FIG. 4 shown a sectional side view of an end clutch valve 10, where a valve spool V has lands L1 and L2 movable in a housing H to selected positions.
A plug PL is located in the right of a valve spool V, and a spring S is mounted elastically between the valve spool and the plug.
In the housing H, a port P1 is connected to a second speed hydraulic pressure line SCV2 of the shift control valve 8, the port P2 is connected to a third speed hydraulic pressure line SCV3, and a port P3 is connected to a fourth speed hydraulic pressure line SCV4.
Also, the port P4 for providing the hydraulic pressure into the end clutch 10 is placed in the housing H. A port P5 operates in the direction of a release of a front clutch 13 and a kick down band brake 16, and is connected to a hydraulic line.
In the first-second speed shift, the end clutch valve 10 explained above becomes ready to make a third speed shift by the valve spool V moved to the right by the second speed hydraulic pressure supplied into the housing H through the port P1.
In the second-third speed shift, the exhausted hydraulic pressure of the front clutch and the kick down band brake 16 is supplied to the inside of the plug PL through the port P5.
At this time, the port P2 is opened by the valve spool moved in the left direction when the sum of the elastic force of a spring S and the hydraulic force operating to the land L2 is larger than the hydraulic force operating at the left of the land L1. Accordingly, the hydraulic pressure supplied through the port P2 is delivered to the end clutch 17 through the port P4.
In the third-fourth speed shift the exhausted hydraulic pressure of the front clutch 13 and the kick down band brake 16 is released, but the end clutch continues operating because the position of a valve spool V becomes the same as the third speed shift by the plug PL moved to the left by the hydraulic pressure being operated to a chamber A.
In the fourth-third speed down-shift, the plug PL is moved to the right by the hydraulic pressure operating through a port P5.
In the third-second speed down-shift the valve spool V is moved to the left by releasing the hydraulic pressure operating through the port P5, and the operating pressure on the end clutch 17 is exhausted quickly through a check ball.
In the second-first speed down-shift, the valve spool V is moved to the left by the elastic force of the spring S, because the hydraulic pressure supplied through the port P1 is drained.
Since the end clutch valve explained above is prepared to make the shift to the third speed by moving the valve spool V by the hydraulic pressure in the second speed, there can occur some problems like the following. The hydraulic pressure operates toward the end clutch, the hydraulic pressure being operated to the other side of the valve spool while the hydraulic pressure operates to one side of the valve spool in the second-third speed shift, and at this time, if the hydraulic pressure line is out of order, a tie-up phenomenon takes place due to sudden movement of the valve.
In addition, it is necessary to use a plug, so that the device is complicated in structure, and is increased in production cost.